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Decipher of the structure and surface chemistry in molybdenum phosphosulfide on electrochemical catalytic hydrogen evolution reaction
Abstract
It has been a fascinating and significant topic that how the chemical composition and surface structure of nanomaterials govern the catalytic performance. In this paper, we deliberately design molybdenum phosphosulfide nanoparticles anchored on the carbon nanotubes (CNTs) and systematically study the correlation between structure/surface composition and the electrochemical hydrogen evolution reaction (HER) activity and stability. We discover that the HER activities show significant enhancement with the incorporation of P in the molybdenum disulfide structure (MoS2|P/CNT) or S in the molybdenum phosphide structure (MoP|S/CNT). The stability of the MoS2|P/CNT catalyst exhibits high stability which is consistent with the pristine MoS2/CNT, while the stability of the MoP/CNT sample is enhanced after the introduction of the S element. The density function theory (DFT) results indicate that the doped P atoms in the MoS2 structure provide more enhanced active sites, leading to promoted HER activity. For the MoP|S/CNT samples, the doped S site is calculated to be less active for HER yet can greatly enhance P site to present better activity. The anion doping effect unveiled here provides insights into molybdenum phosphosulfides for HER and may also be expanded to broad catalyst design for energy related applications.
... This enhancement may be due to the electronic modulation effect of Ponmetal and/or Ssites to facilitate the water dissociation, and in addition the Ps ites could also serve as the active sites for HER. [10,[40][41][42] Moreover, the P-CoNi 2 S 4 catalyst shows superior HER activity and kinetics when compared to some previously reported sulfidebased electrocatalysts (Supporting Information, Table S1). The40hchronopotentiometry test ( Figure S4) also shows the superior catalytic stability of P-CoNi 2 S 4 . ...
Exploring earth‐abundant electrocatalysts with excellent activity, robust stability, and multiple functions is crucial for electrolytic hydrogen generation. Porous phosphorized CoNi2S4 yolk‐shell spheres (P‐CoNi2S4 YSSs) were rationally designed and synthesized by a combined hydrothermal sulfidation and gas‐phase phosphorization strategy. Benefiting from the strengthened Ni³⁺/Ni²⁺ couple, enhanced electronic conductivity, and hollow structure, the P‐CoNi2S4 YSSs exhibit excellent activity and durability towards hydrogen/oxygen evolution and urea oxidation reactions in alkaline solution, affording low potentials of −0.135 V, 1.512 V, and 1.306 V (versus reversible hydrogen electrode) at 10 mA cm⁻², respectively. Remarkably, when used as the anode and cathode simultaneously, the P‐CoNi2S4 catalyst merely requires a cell voltage of 1.544 V in water splitting and 1.402 V in urea electrolysis to attain 10 mA cm⁻² with excellent durability for 100 h, outperforming most of the reported nickel‐based sulfides and even noble‐metal‐based electrocatalysts. This work promotes the application of sulfides in electrochemical hydrogen production and provides a feasible approach for urea‐rich wastewater treatment.
Transition‐metal phosphides prepared from temperature‐programmed reduction (TPR) are generally known to be unstable and prone to surface structure decomposition upon exposure to air. In this work, air‐stable molybdenum phosphide (MoP) was prepared using TPR modified by sulfur. This catalyst was exposed to ambient atmosphere for up to 150 days and still maintained its surface and bulk structures as the fresh sample derived from in situ reduction. The metal phosphosulfide phase generated during TPR not only contributes to the solid structural properties but also exhibits superior catalytic activity in various hydrofining reactions compared to traditional MoP catalysts. Additionally, this preparation strategy was used to synthesize other sulfur‐doped metal phosphides, such as CoP and Cu3P. Both of these catalysts exhibited excellent air‐stability.
Nanoscience and nanotechnology have been undergoing the most explosive growth. However, well-controlled synthesis for manufacturing nanostructures still remains a challenge. In this work, we report a facile procedure to successively prepare the molybdenum dioxide (MoO2), molybdenum carbide (Mo2C) and molybdenum disulfide (MoS2) nanodots on carbon nanotubes (CNT). The prepared samples all possess super fine size. The electrocatalytic properties towards hydrogen evolution reaction (HER) of the three samples are investigated. The results indicate that the MoO2/CNT sample still exhibits very poor HER property, with 420 mV to drive a current density of 10 mA cm⁻², while the Mo2C/CNT and MoS2/CNT samples show highly efficient HER performance, requiring overpotentials of 103 mV and 134 mV to accomplish the same current density, respectively. This work provides a very simple method for preparation of Mo-based nanodot catalysts which can be easily promoted for large-scale production.
Graphical Abstract
The MoO2, Mo2C and MoS2 nanodots are successively prepared on CNT by a facile procedure. The MoO2/CNT sample exhibits very poor HER property, while the Mo2C/CNT and MoS2/CNT samples show highly efficient HER performance.
The development of electrocatalysts with good efficiency, stability, and low cost for hydrogen evolution reaction is significant for the energy future in the world. In the present study, Ag and Pd were electrodeposited on polyaniline (PANI) coated Ni foam and applied for HER in 0.1 M H2SO4. The morphology, structure, and chemical composition of the prepared electrodes were analyzed by FESEM-EDX, BET, and XRD. Electrochemical techniques including cyclic voltammetry (CV), LSV, EIS, and chronoamperometry were used for nickel foam modification and investigation of HER. The obtained results showed that the Pd and AgPd in the presence of PANI deposited on Ni foam have a high current density of 162 and 143 mA·cm⁻², low η10, −137 and −111 mV respectively, high stability, and low charge transfer resistance. According to these advantages, also according to rapid and easy electrode preparation, the proposed electrode can be used as a cathode electrode in the HER process.
Developing high-efficiency multifunctional nanomaterials is promising for wide pH hydrogen evolution reaction (HER) and energy storage but still challenging. Herein, a novel in-situ doping-induced lattice strain strategy of NiCoP/S nanocrystals (NCs) was proposed through using seed crystal conversion approach with NiCo2S4 spinel as precursor. The small amount of S atoms in NiCoP/S NCs perturbed the local electronic structure, leading to the atomic position shift of the nearest neighbor in the protocell and the nanoscale lattice strain, which optimized the H* adsorption free energy and activated H2O molecules, resulting the dramatically elevated HER performance within a wide pH range. Especially, the NiCoP/S NCs displayed better HER electrocatalytic activity than comical 20% Pt/C at high current density in 1 M KOH and natural seawater: it only needed 266 mV vs. reversible hydrogen electrode (RHE) and 660 mV vs. RHE to arrive the current density of 350 mA cm⁻⁻² in 1 M KOH and natural seawater, indicating the application prospect for industrial high current. Besides, NiCoP/S NCs also displayed excellent supercapacitor performance: it showed high specific capacity of 2229.9 F g⁻¹ at 1 A g⁻¹ and energy density of 87.49 Wh kg⁻¹, when assembled into an all-solid-state flexible device, exceeding performance of most transition metal phosphides. This work provides new insights into the regulation in electronic structure and lattice strain for electrocatalytic and energy storage applications.
Exploring earth-abundant electrocatalysts with excellent activity, robust stability, and multiple functions is crucial for electrolytic hydrogen generation. Herein, porous phosphorized CoNi 2 S 4 yolk-shell spheres (P-CoNi 2 S 4 YSSs) are rationally designed and synthesized by a combined hydrothermal sulfidation and gas-phase phosphorization strategy. Benefiting from the strengthened Ni 3+ /Ni 2+ couple, enhanced electric conductivity, and hollow structure, the P-CoNi 2 S 4 YSSs exhibit excellent activity and durability towards hydrogen/oxygen evolution and urea oxidation reactions in alkaline solution, affording low potentials of -0.135 V, 1.512 V, and 1.306 V (versus reversible hydrogen electrode) at 10 mA cm -2 , respectively. Remarkably, when used as the anode and cathode simultaneously, the P-CoNi 2 S 4 catalyst merely requires a cell voltage of 1.544 V in water splitting and 1.402 V in urea electrolysis to attain 10 mA cm -2 with excellent durability for 100 h, outperforming most of the reported nickel-based sulfides and even noble-metal-based electrocatalysts. This work therefore not only promotes the application of sulfides in electrochemical hydrogen production but also provides a feasible approach for urea-rich wastewater treatment.
Metal phosphides (MPs) with unique and desirable physicochemical properties provide promising potential in practical applications, such as the catalysis, gas/humidity sensor, environmental remediation, and energy storage fields, especially for transition metal phosphides (TMPs) and MPs consisting of group IIIA and IVA metal elements. Most studies, however, on the synthesis of MP nanomaterials still face intractable challenges, encompassing the need for a more thorough understanding of the growth mechanism, strategies for large-scale synthesis of targeted high-quality MPs, and practical achievement of functional applications. This review aims at providing a comprehensive update on the controllable synthetic strategies for MPs from various metal sources. Additionally, different passivation strategies for engineering the structural and electronic properties of MP nanostructures are scrutinized. Then, we showcase the implementable applications of MP-based materials in emerging sustainable catalytic fields including electrocatalysis, photocatalysis, mild thermocatalysis, and related hybrid systems. Finally, we offer a rational perspective on future opportunities and remaining challenges for the development of MPs in the materials science and sustainable catalysis fields.
The interfacial charge of active centers in heterogeneous catalysts modulates the sorption-desorption of intermediates. However, it is challenging to bridge the interfacial charge distribution and catalytic activity. Herein, a facile galvanostatic deposition strategy is used to anchor cost-effective ruthenium (Ru) single atoms (SAs) into MoS2/MoP heterosturctures on carbon cloth ([email protected]2/MoP/Ru SAs). Electrochemical test of [email protected]2/MoP/Ru SAs reveals superior alkaline hydrogen evolution reaction (HER) activity with low overpotential of 45 and 114 mV at the current of –10 and –100 mA cmgeo–2, respectively. The [email protected]2/MoP/Ru SAs also exhibit high stability for at least 100 h. Dual-pathway kinetic analysis and density functional theory (DFT) calculation clearly unravel the importance of synergy and charge redistribution between the interfaces of MoS2/MoP and Ru SAs, which modulate adsorption and desorption of intermediates. This work correlates the synergy in conjunction with interfacial charge distribution to promote catalytic activity, taking as a guide to get new insight into the design of advanced electrocatalysts
Herein, we report a hydrogen-assisted selective dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb) to 2,3,3,3-tetrafluoropropene (HFO-1234yf) over nickel phosphides (Ni2P, Ni12P5 and Ni3P) catalysts. The Ni3P catalyst exhibited higher activity and HFO-1234yf selectivity than Ni12P5 and Ni3P catalysts. An induction period over Ni3P was observed during the initial 15 h under reaction conditions of 300 oC and H2/HCFC-244bb of 1.5, then a steady HCFC-244bb conversion ∼42% and HFO-1234yf selectivity ∼88% was obtained within the rest of 105 h. The catalysts were characterized by in situ temperature-programmed desorption analysis, X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The in situ H2-TPD results reveal that Ni3P was capable of forming larger amount of active hydrogen species than the other nickel phosphides, but by comparing the desorption temperature the reactivity of active hydrogen species on Ni3P was weaker than those formed on Ni12P5 and Ni2P, leading to higher activity and HFO-1234yf selectivity of Ni3P. The theoretical calculations also find that the adsorption energy of H2 over Ni3P is lower than those over Ni12P5 and Ni2P. XPS and TEM-mapping show that a surface chlorination occurred on Ni3P during the initial stage of reaction, resulting in an increase of surface acidity. Thus, the enhanced catalytic efficiency of Ni3P during the induction period can be attributed to a synergism between the metal sites and the in situ formed weak acid sites, further promoting the C-Cl bond scission by active H species and inhibiting the deep-hydrogenation.
Due to the rapid development of alkaline polymer electrolyte fuel cells and water splitting, it is becoming increasingly urgent to develop non-precious metal electrocatalysts for the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) in alkaline medium. Herein, Co2P/CoP hybrid is synthesized from cobalt carbonate hydroxide (CoCH) precursor, and further evaluated for the electrocatalytic HOR and HER in alkaline electrolytes. Specifically, benefiting from the reasonable hybrid structure that integrate suitable hydrogen adsorption energy of CoP and excellent conductivity of Co2P, Co2P/CoP hybrid exhibits excellent catalytic activities. The Co2P/[email protected] hybrid has impressive HER activity, with a current density of -10 mA cm⁻² at the overpotentials of -61 mV and the Tafel slope of 55.1 mV dec⁻¹, which can compete with recently reported transition metal phosphides and cobalt-based catalysts. In addition, the exchange current density of Co2P/[email protected] hybrid is ∼0.82 mA cm⁻² for HOR, which is close to commercial Pt/C catalyst (∼1.14 mA cm⁻²).
Despite promising characteristics such as high specific energy and low cost, current Li–S batteries fall short in cycle life. Improving the cycling stability of S cathodes requires immobilizing the lithium polysulfide (LPS) intermediates as well as accelerating their redox kinetics. Although many materials have been explored for trapping LPS, the ability to promote LPS redox has attracted much less attention. Here, we report for the first time on transition metal phosphides as effective host materials to enhance both LPS adsorption and redox. Integrating MoP-nanoparticle-decorated carbon nanotubes with S deposited on graphene oxide, we enable Li–S battery cathodes with substantially improved cycling stability and rate capability. Capacity decay rates as low as 0.017% per cycle over 1,000 cycles can be realized. Stable and high areal capacity (>3 mAh·cm⁻²) can be achieved under high mass loading conditions. Comparable electrochemical performance can also be achieved with analogous material structures based on CoP, demonstrating the potential of metal phosphides for long-cycle Li–S batteries.
Molybdenum disulfides and carbides are effective catalysts for hydrogenation and hydridesulfurization, where MoS2 nanostructures are also highly promising materials for lithium ion batteries. High surface-to-volume ratio and strong interactions with conducting networks are crucial factors for their activities. A new hybrid structure of multi-walled carbon nanotube (MWCNT) with alternate MoC nanoparticles and MoS2 nanosheets (MoS2+MoC-MWCNT) has been synthesized by controlled carburization of core shell MoS2-MWCNT hybrid nanotubes and demonstrated by HRTEM, FFT, XRD, and Raman scattering. The MoS2 nanosheets (~10 nm) remain tightly connected to MWCNT surfaces with {001} planes in parallel to MWCNT walls and the highly crystallized α-MoC particles (~10 nm) are adhered to MWCNTs at angles of 60-80º between {111} planes and MWCNT walls. The electrochemical performances of the hybrid structures have been demonstrated as anodes for lithium ion batteries to be significantly increased by breaking MoS2 nanotubes into nanosheets (patches) on MWCNT surfaces, especially at high current rates. The specific capacities of MoS2+MoC-MWCNT sample with ~23% MoS2 have been demonstrated to be higher than those of MoS2-MWCNTs containing ~70% MoS2.
Electrochemical production of hydrogen from water has been directed to the search for non-noble metal based and earth-abundant catalysts. In this work, we propose a novel cost-effective catalyst, molybdenum phosphide that exhibits high activity towards the hydrogen evolution reaction (HER) in both acid and alkaline media even in bulk form. Comparative analysis of Mo, Mo3P and MoP as catalysts for HER clearly indicates that phosphorization can potentially modify the properties of the metal and different degrees of phosphorization lead to distinct activities and stabilities. Theoretical calculations by density functional theory also show that a simple phosphorization of molybdenum to form MoP introduces a good ‘H delivery’ system which attains nearly zero binding to H at a certain H coverage. With the combination of experimental results and theoretical calculations, this work has enlightened a new way of exploring cost-effective catalysts for HER.
We present a method for calculating the stability of reaction intermediates of electrochemical processes on the basis of electronic structure calculations. We used that method in combination with detailed density functional calculations to develop a detailed description of the free-energy landscape of the electrochemical oxygen reduction reaction over Pt(111) as a function of applied bias. This allowed us to identify the origin of the overpotential found for this reaction. Adsorbed oxygen and hydroxyl are found to be very stable intermediates at potentials close to equilibrium, and the calculated rate constant for the activated proton/ electron transfer to adsorbed oxygen or hydroxyl can account quantitatively for the observed kinetics. On the basis of a database of calculated oxygen and hydroxyl adsorption energies, the trends in the oxygen reduction rate for a large number of different transition and noble metals can be accounted for. Alternative reaction mechanisms involving proton/electron transfer to adsorbed molecular oxygen were also considered, and this peroxide mechanism was found to dominate for the most noble metals. The model suggests ways to improve the electrocatalytic properties of fuel-cell cathodes.
The identification of the active sites in heterogeneous catalysis requires a combination of surface sensitive methods and reactivity studies. We determined the active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) by atomically resolving the surface of this catalyst before measuring electrochemical activity in solution. By preparing MoS2 nanoparticles of different sizes, we systematically varied the distribution of surface sites on MoS2 nanoparticles on Au(111), which we quantified with scanning tunneling microscopy. Electrocatalytic activity measurements for hydrogen evolution correlate linearly with the number of edge sites on the MoS2 catalyst.
Design of highly efficient catalysts has already been a challenge in the exploration of renewable energies based on nanotechnologies. Herein, a feasible strategy of three-dimensional (3D)/two-dimensional (2D) nanojunctions was employed to achieve a prominently enhanced activity in both solar hydrogen evolution and electrochemical hydrogen generation from water splitting. Flower-like MoS2 nanoparticles with thin-layers were fabricated using a one-pot hydrothermal process and were further attached to g-C3N4 nanosheets via their (002) crystal planes to form an intimate face-to-face contact. The hybrid catalysts exhibited a red-shift to the visible light region with an enhanced absorption capacity. At the optimal loading of 0.5 wt% MoS2, MoS2/g-C3N4 exhibited the highest photocatalytic H2 evolution rate of 867.6 μmol h⁻¹ g⁻¹ under simulated sunlight irradiations, which is 2.8 times as high as that of pure g-C3N4. Furthermore, the average photocatalytic H2 evolution rate was elevated to ca. 5 times as high as that of pure g-C3N4 under visible light irradiations. The synergistic effect responsible for the enhanced HER (hydrogen evolution reaction) performance might be originated from the intimate interface between the light-harvesting g-C3N4 and MoS2 as the active sites with the decreased overpotential, lowered charge-transfer resistance and increased electrical conductivity, leading to a more efficient charge separation and a higher reductive potential. In addition, the lower overpotential and smaller Tafel slope on 0.5 wt% MoS2/g-C3N4 lead to the enhancement of electrochemical HER performance compared to pure g-C3N4. This work provides a feasible protocol for rational design of highly efficient HER electrocatalysts and photocatalysts towards future energy innovation.
Electrochemical water splitting with non-noble metal catalysts provides an eco-friendly strategy for renewable production of hydrogen. In this study, the MoP@C@rGO composite was prepared via mild reactions through chemical bath and post annealing process. With the assistance of citric acid, the MoP@C@rGO composite containing ultrafine MoP nanoparticles with size of 3 nm anchored on two-dimensional C/rGO nanosheets has been obtained. The chelation effect with citric acid and the merits of rGO not only lead to affordable active sites but also improved the electrical conductivity and the stability at the same time. Serving as hydrogen evolution reaction (HER) electrocatalyst, the MoP@C@rGO composite presents a small overpotential of 168.9 mV at 10 mA cm-2. Its durability is more stable than that of the pure MoP, comparing samples of MoP@C and MoP@rGO. The relative high activity, stable performance as well as the simple preparation process make the MoP@C@rGO composite promising HER electrocatalyst.
The molybdenum phosphide-based catalysts have recently exhibited excellent catalytic activities for hydrogen evolution reaction (HER) in wide pH range conditions, the intrinsic reaction mechanism, on the other hand, has not been well established. Herein, by employing the MoP as the prototypical molybdenum phosphide-based catalyst, HER activities in both acid and neutral conditions were studied by conducting periodic density functional theory (DFT) calculations.. Thermodynamic analysis of hydrogen atoms absorbed on both P- and Mo-terminated surfaces were compared, as well as all the reaction energy and activation energy barriers for reactions involved in the HER process. Calculation results revealed that, in an acid condition, the Volmer-Heyrovsky and Vomer-Tafel reaction mechanisms were dominated on the P-terminated and Mo-terminated catalyst surfaces, where Heyrovsky and Vomer reactions were the rate-determining step, respectively. Additionally, water splitting was introduced to current reaction mechanism and a small reaction activation energy barrier was revealed on the P-terminated surface. Besides, a relevant small activation energy was obtained in Tafel reaction on the defect of the P-terminated surface in a neutral solution. Theoretical results proved that HER could take place readily on both P- and Mo-terminated catalyst surfaces via different reaction mechanisms in the acid condition from the view of atom scale. More important, computational results uncovered that HER could also occur on the P-terminated surface with the assistance of surface defect in the neutral condition, which shed new light on HER mechanism on transition metal phosphite-based catalysts. The doping effect on HER activity was further investigated in theory and calculation results indicated that catalytic performance could be improved by substitutional doping of the Mo atom with metals like Mn and W.
The layer‐structured MoS2 is a typical hydrogen evolution reaction (HER) electrocatalyst but it possesses poor activity for the oxygen evolution reaction (OER). In this work, a cobalt covalent doping approach capable of inducing HER and OER bifunctionality into MoS2 for efficient overall water splitting is reported. The results demonstrate that covalently doping cobalt into MoS2 can lead to dramatically enhanced HER activity while simultaneously inducing remarkable OER activity. The catalyst with optimal cobalt doping density can readily achieve HER and OER onset potentials of −0.02 and 1.45 V (vs reversible hydrogen electrode (RHE)) in 1.0 m KOH. Importantly, it can deliver high current densities of 10, 100, and 200 mA cm−2 at low HER and OER overpotentials of 48, 132, 165 mV and 260, 350, 390 mV, respectively. The reported catalyst activation approach can be adapted for bifunctionalization of other transition metal dichalcogenides. A cobalt covalent doping catalyst activation approach to induce hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) bifunctionality of MoS2 is proposed and experimentally validated, demonstrating superior bifunctional electrocatalytic activities with great application potential for overall water splitting in alkaline media.
Molybdenum disulfide (MoS2) presents a promising catalyst to replace state-of the-art platinum (Pt) for hydrogen evolution reaction (HER), but it still lacks an effective way due to the catalytically inert basal plane. Herein, we report a rational design of MoS2 nanomesh that possesses evenly distributed holes and defects to make full use of the 2H-MoS2 basal planes by combining ball-milling with ultrasonic methods. The exfoliation of muti-layer MoS2 to fewer layer or enven monolayer is proceed in pure water without using any chemicals or surfactants. The great advantage of the catalyst is the monolayer, holey and defective structure, which maximizing the synergistic activity for both electrocatalytic and photocatalytic HER performances. Impressively, the MoS2 nanomesh renders outstanding electrocatalytic HER activity with an overpotential of 160 mV at a current density of 10 mV cm⁻², and a small Tafel slope of 46 mV decade⁻¹. The photocatalytic H2 evolution rate is about 4.84 mmol h⁻¹ when working with Eosin Y as an organic photosensitizer. Additionally, this catalyst shows excellent cycle stability in the electrochemical and photocatalytic reactions. This present work put a new insight into the large-scale production of chemically active 2H MoS2-based catalysts for HER.
Recently, molybdenum sulfide with its amorphous counterpart was found to hold a high activity versus the hydrogen evolution reaction (HER), making it a high potential material to explore new HER catalysts. Here we present a facile chemical method to synthesize ultra-small freestanding amorphous molybdenum sulfide (a-MoSx) colloidal nanodots with diameter of lower than 2 nm. Electrocatalytic HER tests show that freestanding a-MoSx colloidal nanodots exhibit an enhanced catalytic hydrogen activity in stark in contrast with in-situ annealed c-MoS2. When applied as a co-catalyst in photocatalytic HER, ultra-small a-MoSx nanodots could form a compact interface with the TiO2 when assisted by a bifunctional molecular linker, as the mercaptopropionic acid (MPA), which facilitates the decrease of the interfacial Schottky barrier occurring between the two components and allows for a fast injection of photo-excited electrons from the photoharvester into the co-catalyst. Our results demonstrate that the drastic enhancement of the photocatalytic H2 promotion rate of a-MoSx@MPA-TiO2 is mainly provided by unsaturated Mo(IV) active sites generated by the in-situ reduction during the photocatalytic HER process. The synergistic effect of generated unsaturated Mo(IV) sites and the presence of more exposed intrinsic active edges further promotes the enhancement of the catalytic H2 activity on a-MoSx nanodots.
Electrochemical water splitting has been highly valued as a clean and sustainable method to produce hydrogen with high purity and large quantity. Platinum (Pt) possesses excellent performance for hydrogen evolution reaction (HER), however, the expensiveness and rareness still restricts its broad application. Here, an environmentally-friendly and template-free method is developed to synthesize N-doped molybdenum carbide in three different forms: nanobelts, nanorods and nanoparticles. During the synthesis, no additional acid or alkali aqueous solution is used and the morphology is controlled by adjusting water content and treatment time. The corresponding physicohemical and electrochemical results display that the nanobelts with porous nanostructure exhibit excellent activity and good stability for HER both in acidic and alkaline electrolytes. In the latter case (1.0 M KOH aqueous solution), nanobelts show a small onset potential value (–52 mV), yield a current density of 10 mA cm⁻² at a relatively low overpotential (110 mV) and exhibit a low Tafel slope (49.7 mV dec⁻¹). From the obtained results is deduced that this is a facile way to prepare cost-effective molybdenum carbide with high efficiency for hydrogen evolution.
Molybdenum disulfide (MoS2) has been considered as a promising alternative to platinum (Pt)-based catalyst for hydrogen evolution reaction (HER) due to its low cost and high catalytic activity. However, stable 2H phase of MoS2 (2H-MoS2) exhibits low catalytic activity in HER due to the inert basal plane and S-edge. Thus, to exploit the basal plane and S-edge for additional electrocatalytic activity, a facile strategy is developed to prepare P-doped 2H-MoS2 film on conductive substrate via low-temperature heat treatment. Due to the inherent difficulty of P-doping into MoS2 crystal structure, oxygen (O)-doping is utilized to aid the P-doping process, as supported by the first-principles calculations. Interestingly, P-doping could dramatically reduce Mo valence charge, which results in the functionalization of the inert MoS2 basal plane and S-edge. In agreement with simulation results, P-doped 2H-MoS2 electrode exhibits enhanced catalytic performance in H2 generation with low onset potential (130 mV) and small Tafel slope of 49 mV dec⁻¹. The enhanced catalytic performance arises from the synergistic effect of the activated basal plane, S-edge, and Mo-edge sites, leading to favorable hydrogen adsorption energies. Most importantly, improved cyclic stability is achieved, which reveals chemically inert properties of P-doped 2H-MoS2 in acidic electrolyte.
Herein, the authors explicitly reveal the dual-functions of N dopants in molybdenum disulfide (MoS2) catalyst through a combined experimental and first-principles approach. The authors achieve an economical, ecofriendly, and most efficient MoS2-based hydrogen evolution reaction (HER) catalyst of N-doped MoS2 nanosheets, exhibiting an onset overpotential of 35 mV, an overpotential of 121 mV at 100 mA cm⁻² and a Tafel slope of 41 mV dec⁻¹. The dual-functions of N dopants are (1) activating the HER catalytic activity of MoS2 S-edge and (2) enhancing the conductivity of MoS2 basal plane to promote rapid charge transfer. Comprehensive electrochemical measurements prove that both the amount of active HER sites and the conductivity of N-doped MoS2 increase as a result of doping N. Systematic first-principles calculations identify the active HER sites in N-doped MoS2 edges and also illustrate the conducting charges spreading over N-doped basal plane induced by strong Mo 3d–S 2p–N 2p hybridizations at Fermi level. The experimental and theoretical research on the efficient HER catalysis of N-doped MoS2 nanosheets possesses great potential for future sustainable hydrogen production via water electrolysis and will stimulate further development on nonmetal-doped MoS2 systems to bring about novel high-performance HER catalysts.
The excellent catalytic activity of metallic MoS2 edges for the hydrogen evolution reaction (HER) has led to substantial efforts towards increasing the edge concentration. The 2H basal plane is less active for the HER because it is less conducting and therefore possesses less efficient charge transfer kinetics. Here we show that the activity of the 2H basal planes of monolayer MoS2 nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving the electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. Phase-engineered low-resistance contacts on monolayer 2H-phase MoS2 basal plane lead to higher efficiency of charge injection in the nanosheets so that its intrinsic activity towards the HER can be measured. We demonstrate that onset potentials and Tafel slopes of ∼-0.1 V and ∼50 mV per decade can be achieved from 2H-phase catalysts where only the basal plane is exposed. We show that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal plane. Our results provide new insights into the role of contact resistance and charge transport on the performance of two-dimensional MoS2 nanosheet catalysts for the HER.
Preparation of electrocatalysts with high activity and low cost are essential for mass production of hydrogen. However, preparation of such catalyst are still highly challenging thus far. In this paper, we focus on preparation of a three- dimensional CNTs aerogel/MoSx catalyst by using solvothermal process. The MoSx material has successfully combined with three- dimensional CNTs aerogel and creates a sufficient active site exposure as well as 3D conductive networks for fast charge transport. Due to this exhibited high activity for HER with a small onset over potential of ∼150 mV, a Tafel slope of 62 mV dec−1, and an exchange current density of 6.35 mA cm−2. The catalysts also show excellent stability during long-term 1000 cycles and electrolysis confirm the durability of the catalyst. The enhanced performance is attributed to synergistic effects of CNTs aerogel and MoSx, which enhance the activities for both components for HER.
Molybdenum disulfide (MoS2) has attracted extensive attention as a non-noble metal electrocatalyst for hydrogen evolution reaction (HER). Controlling skeleton structure at the nano scale is paramount to increase the number of active sites at the surface. However, hydrothermal synthesis favours the presence of the basal plane, limiting the efficiency of catalytic reaction. In this work, perfect hollow MoS2 microsphere capped by hollow MoS2 nanospheres (hH-MoS2) were obtained for the first time, which propose an opportunity for improving the HER electrocatalytic performance. Benefiting from the controllable hollow skeleton structure and large exposed edge sites, high-efficiency HER activity was obtained for stacked MoS2 thin shells with a mildly degree of disorder, proving rich active sites and the validity of the combined structural. In general, the obtained hollow micro/nano MoS2 nanomaterial exhibits optimized electrocatalytic activity for HER with onset overpotential as low as 112 mV, low Tafel slope of 74 mV dec-1, high current density of 10 mA cm-2 at η = 214 mV and high TOF of 0.11 H2 s-1 per active site at η = 200 mV.
Ultrathin two-dimensional (2D) nanosheets, such as graphene and MoS2, which are demonstrated to be fundamentally and technologically important in many applications, have emerged as a unique family of nanomaterials in chemistry and material science over the past decade. The single-crystalline nature and ultrathin thickness of these 2D nanosheets make them ideal templates for the epitaxial deposition of nanostructures, which offer many possibilities to engineer microsized 2D p-n hetero-junctions at atomic/nanometer scale. This Perspective aims to provide information on the epitaxial growth of hetero-nanostructures based on ultrathin 2D nanosheets. Various methods for the epitaxial growth of nanostructures based on ultrathin 2D nanosheets or in situ growth of lateral or vertical epitaxial 2D semiconductor hetero-nanostructures are introduced. The advantages of these 2D epitaxial hetero-nanostructures for some applications, such as electronics, optoelectronics, and electrocatalysis, are also presented. On the basis of the current status of 2D epitaxial hetero-nanostructures, the future prospects of this promising area are discussed.
Electrocatalytic hydrogen evolution has been regarded as a promising strategy to realize efficient hydrogen production to face the energy crisis in the future. Hence, the design of hydrogen-evolving catalysts with high activity and low cost is imperative. In this Minireview article, state-of-the-art electrocatalysts for the hydrogen evolution reaction (HER) are overviewed, and the strategies for constructing ordered and disordered HER electrocatalysts are summarized in detail. By means of facet engineering, nanoscale, polymorph engineering accompanied by interface engineering, HER catalysts with an ordered structure could be optimized. For designing disordered catalysts, defect engineering, amorphization, elemental doping, and surface modification, as well as constructingan alloyed structure, could be effective to realize the beneficial modulation of active sites and electronic structure. This Minireview provides a structural perspective for the design of efficient HER electrocatalysts in the future.
Density functional theory is used to investigate the adsorption and structural properties of layered transition-metal sulfide (TMS) catalysts. We considered both the (10(1) over bar 0) M-edge and ((1) over bar 010) S-edge terminations for a wide range of pure and doped TMSs, determined their sulfur coverage under realistic operating conditions (i.e, steady-state structures), and calculated an extensive set of chemisorption energies for several important reactions. On the basis of these results, we show that the d-band center, epsilon(d), of the edge-most metal site at 0 ML sulfur coverage is a general electronic descriptor for both structure and adsorption energies, which are known to describe catalytic activity. A negative linear correlation between adsorbate-S binding and S-metal binding allows epsilon(d) to describe the adsorption of species on both metal and sulfur sites. Our results provide a significant simplification in the understanding of structure-activity relationships in TMSs and provides guidelines for the rational design and large-scale screening of these catalysts for various processes.
Outstanding magnetic properties are highly desired for two-dimensional ultrathin semiconductor nanosheets. Here, we propose a phase incorporation strategy to induce robust room-temperature ferromagnetism in nonmagnetic MoS2 semiconductor. A two-step hydrothermal method was used to intentionally introduce sulfur vacancies in 2H-MoS2 ultrathin nanosheet host, which prompt the transformation of the surrounding 2H-MoS2 local lattice into a trigonal (1T-MoS2) phase. 25% 1T-MoS2 phase incorporation in 2H-MoS2 nanosheets can enhance the electron carrier concentration by an order, introduce a Mo4+ 4d energy state within the bandgap, and create a robust intrinsic ferromagnetic response of 0.25 B/Mo by the exchange interactions between sulfur vacancy and the Mo4+ 4d bandgap state at room temperature. This design opens up new possibility for effective manipulation of exchange interactions in two-dimensional nanostructures.
Providing energy for a population projected to reach 9 billion people within the middle of this century is one of the most pressing societal issues. Burning fossil fuels at a rate and scale that satisfy our near-term demand will irreversibly damage the living environment. Among the various sources of alternative and CO2-emission-free energies, the sun is the only source that is capable of providing enough energy for the whole world. Sunlight energy, however, is intermittent and requires an efficient storage mechanism. Sunlight-driven water splitting to make hydrogen is widely considered as one of the most attractive methods for solar energy storage. Water splitting needs a hydrogen evolution catalyst to accelerate the rate of hydrogen production and to lower the energy loss in this process. Precious metals such as Pt are superior catalysts, but they are too expensive and scarce for large-scale applications.
We report the preparation and characterization of highly efficient and robust photocathodes based on heterostructures of chemically exfoliated metallic 1T-MoS2 and planar p-type Si for solar-driven hydrogen production. Photocurrents up to 17.6 mA/cm(2) at 0 V vs reversible hydrogen electrode were achieved under simulated 1 sun irradiation, and excellent stability was demonstrated over long-term operation. Electrochemical impedance spectroscopy revealed low charge-transfer resistances at the semiconductor/catalyst and catalyst/electrolyte interfaces, and surface photoresponse measurements also demonstrated slow carrier recombination dynamics and consequently efficient charge carrier separation, providing further evidence for the superior performance. Our results suggest that chemically exfoliated 1T-MoS2/Si heterostructures are promising earth-abundant alternatives to photocathodes based on noble metal catalysts for solar-driven hydrogen production.
We report the synthesis of hetero-dimensional nanostructures of MoS2 quantum dots interspersed few-layered sheets of MoS2, using liquid exfoliation technique in organic solvents. This unique hybrid morphology results from the optimized experimental conditions involving bath sonication followed by ultrasound probe sonication. We show that such hetero-dimensional hybrid materials could easily be extracted from the solvent as precipitates when post-treated with less polar volatile solvents such as chloroform. Such tailored MoS2 nanostructures, when directly used as electrodes for hydrogen evolution reaction (HER), showed excellent electrocatalytic activity with low overpotential. Hence, we believe this could lead to large scale synthesis of liquid-exfoliated layered nanostructures for their potential applications.
Identifying and understanding the active sites responsible for reaction turnover is critical to developing improved catalysts. For the hydrogen-evolution reaction (HER), MoS2 has been identified as an active non-noble-metal-based catalyst. However, only edge sites turnover the reaction because the basal planes are catalytically inert. In an effort to develop a scalable HER catalyst with an increased number of active sites, herein we report a Mo-S catalyst (supported thiomolybdate [Mo3S13](2-) nanoclusters) in which most sulfur atoms in the structure exhibit a structural motif similar to that observed at MoS2 edges. Supported sub-monolayers of [Mo3S13](2-) nanoclusters exhibited excellent HER activity and stability in acid. Imaging at the atomic scale with scanning tunnelling microscopy allowed for direct characterization of these supported catalysts. The [Mo3S13](2-) nanoclusters reported herein demonstrated excellent turnover frequencies, higher than those observed for other non-precious metal catalysts synthesized by a scalable route.
We report chemically exfoliated MoS2 nanosheets with a very high concentration of metallic 1T phase using a solvent free intercalation method. After removing the excess of negative charges from the surface of the nanosheets, highly conducting 1T phase MoS2 nanosheets exhibit excellent catalytic activity toward the evolution of hydrogen with a notably low Tafel slope of 40 mV/dec. By partially oxidizing MoS2, we found that the activity of 2H MoS2 is significantly reduced after oxidation, consistent with edge oxidation. On the other hand 1T MoS2 remains unaffected after oxidation suggesting that edges of the nanosheets are not the main active sites. The importance of electrical conductivity of the two phases on the hydrogen evolution reaction activity has been further confirmed by using carbon nanotubes to increase the conductivity of 2H MoS2.
The surface of MoP becomes sulfided during hydrodesulfurization (HDS) of dibenzothiophene (DBT), and the HDS activity increases with time on stream, showing that the sulfided MoP surface is more active than the fresh MoP surface. MoP pretreated with H2S/H2 under HDS reaction conditions showed the same activity increase as fresh MoP, but XPS did not show any sulfur at the surface of the pretreated MoP. Hence, the sulfur that is incorporated into the MoP surface during the HDS of DBT originates from DBT rather than from H2S.
Promising catalytic activity from molybdenum disulfide (MoS2) in the hydrogen evolution reaction (HER) is attributed to active sites located along the edges of its two-dimensional layered crystal structure, but its performance is currently limited by the density and reactivity of active sites, poor electrical transport, and inefficient electrical contact to the catalyst. Here we report dramatically enhanced HER catalysis (an electrocatalytic current density of 10 mA/cm(2) at a low overpotential of ‒187 mV vs. RHE and a Tafel slope of 43 mV/decade) from metallic nanosheets of 1T-MoS2 chemically exfoliated via lithium intercalation from semiconducting 2H-MoS2 nanostructures grown directly on graphite. Structural characterization and electrochemical studies confirm that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics, low-loss electrical transport, and possess a proliferated density of catalytic active sites. These distinct and previously unexploited features of 1T-MoS2 make these metallic nanosheets a highly competitive earth-abundant HER catalyst.
Improving both the activity and the stability of the cathode catalyst in platinum-based polymer electrolyte fuel cells is a key technical challenge. Here, we synthesize a high surface area meso-structured Pt thin film that exhibits higher specific activity for the oxygen reduction reaction (ORR) than commercial carbon-supported Pt nanoparticles (Pt/C). An accelerated stability test demonstrates that the meso-structured Pt thin film also displays significantly enhanced stability as compared to the commercial Pt/C catalyst. Our study reveals the origin of the high turnover frequency (TOF), and excellent durability is attributed to the meso-structure, which yields a morphology with fewer undercoordinated Pt sites than Pt/C nanoparticles, a key difference with substantial impact to the surface chemistry. The improved catalyst activity and stability could enable the development of a high-performance gas diffusion electrode that is resistant to corrosion even under the harsh conditions of start-up, shut-down, and/or hydrogen starvation.
Silica-supported molybdenum phosphide (MoP/SiO2) catalysts have been prepared and characterized by X-ray diffraction (XRD), pulsed chemisorption (CO and O2), scanning and transmission electron microscopy (SEM and TEM, respectively), and X-ray photoelectron spectroscopy (XPS). XRD and TEM analysis of MoP/SiO2 catalysts confirmed the presence of MoP crystallites dispersed on the surface of the silica support, while SEM energy dispersive X-ray microanalysis indicated the bulk composition of the supported MoP particles to be 12.7 atom% Mo and 14.1 atom% P. XPS analysis of a passivated 25 wt% MoP/SiO2 catalyst indicated the presence of two kinds of Mo species as well as phosphide and phosphate species at the catalyst surface. Thiophene hydrodesulfurization (HDS) activities were measured for 15 and 25 wt% MoP/SiO2 catalysts, and for a sulfided Mo/SiO2 catalyst with a Mo loading similar to that of the lower loading MoP catalyst. The 15 wt% MoP/SiO2 catalyst, when pretreated only by degassing in flowing He, was nearly four times more active than the sulfided Mo/SiO2 catalyst after 150 h on-stream. Following an initial decline in HDS activity during the first 3 h of measurement, the MoP/SiO2 catalyst displayed an unusual trend of HDS activity that increased monotonically as a function of time on-stream.
States of chemisorbed H that can be involved in the mechanism of the cathodic H2 evolution reaction (HER) at metals, specially Pt, and the reverse oxidation reaction (HOR), are examined. Particular attention is paid to possible differences between underpotential-deposited (UPD) H, electrosorbed at potentials below the hydrogen reversible potential, and so-called overpotential-deposited (OPD) H that is involved, kinetically, as an intermediate in the HER. UPD H is involved in the HOR, following dissociative chemisorption of H2, at potentials positive to the RHE potential. The roles of diffusion-control involving H2, both in the HER and the HOR, are discussed in the light of experimental results for cathodic and anodic polarization. Values of exchange current-density, jo, for the HER/HOR at equilibrium depend widely on the adsorptive and electronic properties of the metal, often representable as a ‘volcano’ relation with respect to metal-to-H bond energy. The origin of such relations, especially at the catalytic noble metals, is examined in terms of UPD and OPD states of H. Mechanistic and kinetic aspects of the HER and HOR are treated and their sensitivity to presence of CO and to surface structure at Pt single-crystal faces is reviewed.
Fueled by concerns about urban air pollution, energy security, and climate change, the notion of a “hydrogen economy” is moving beyond the realm of scientists and engineers and into the lexicon of political and business leaders. Interest in hydrogen, the simplest and most abundant element in the universe, is also rising due to technical advances in fuel cells — the potential successors to batteries in portable electronics, power plants, and the internal combustion engine. But where will the hydrogen come from? Government and industry, keeping one foot in the hydrocarbon economy, are pursuing an incremental route, using gasoline or methanol as the source of the hydrogen, with the fuel reformed on board vehicles. A cleaner path, deriving hydrogen from natural gas and renewable energy and using the fuel directly on board vehicles, has received significantly less support, in part because the cost of building a hydrogen infrastructure is widely viewed as prohibitively high. Yet a number of recent studies suggest that moving to the direct use of hydrogen may be much cleaner and far less expensive. Just as government played a catalytic role in the creation of the Internet, government will have an essential part in building a hydrogen economy. Research and development, incentives and regulations, and partnerships with industry have sparked isolated initiatives. But stronger public policies and educational efforts are needed to accelerate the process. Choices made today will likely determine which countries and companies seize the enormous political power and economic prizes associated with the hydrogen age now dawning.
Advanced materials for electrocatalytic and photoelectrochemical water splitting are central to the area of renewable energy. In this work, we developed a selective solvothermal synthesis of MoS(2) nanoparticles on reduced graphene oxide (RGO) sheets suspended in solution. The resulting MoS(2)/RGO hybrid material possessed nanoscopic few-layer MoS(2) structures with an abundance of exposed edges stacked onto graphene, in strong contrast to large aggregated MoS(2) particles grown freely in solution without GO. The MoS(2)/RGO hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) relative to other MoS(2) catalysts. A Tafel slope of ∼41 mV/decade was measured for MoS(2) catalysts in the HER for the first time; this exceeds by far the activity of previous MoS(2) catalysts and results from the abundance of catalytic edge sites on the MoS(2) nanoparticles and the excellent electrical coupling to the underlying graphene network. The ∼41 mV/decade Tafel slope suggested the Volmer-Heyrovsky mechanism for the MoS(2)-catalyzed HER, with electrochemical desorption of hydrogen as the rate-limiting step.
Over the past decade the theoretical description of surface reactions has undergone a radical development. Advances in density functional theory mean it is now possible to describe catalytic reactions at surfaces with the detail and accuracy required for computational results to compare favourably with experiments. Theoretical methods can be used to describe surface chemical reactions in detail and to understand variations in catalytic activity from one catalyst to another. Here, we review the first steps towards using computational methods to design new catalysts. Examples include screening for catalysts with increased activity and catalysts with improved selectivity. We discuss how, in the future, such methods may be used to engineer the electronic structure of the active surface by changing its composition and structure.
Energy storage technology increases the value of all renewable energy supplies whether they are centralized or decentralized. However, centralized (over the grid) or decentralized energy distribution results in different targets for energy storage as a result of different time scales and the nature of the demand. Most grid-based storage mechanisms are mechanical and they span storage needs, with time scales of microseconds to days. The most sustainable source of protons and electrons for solar fuels production is water, which when split by an OER catalyst delivers oxygen and the requisite four electrons and protons needed for fuels production. The electrons and protons may be directly combined to produce H2 by a HER catalyst or, with future research discovery, combined with CO2 to furnish a liquid fuel. The best Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER) catalysts are heterogeneous when a normalized comparison of performance is made between homogeneous and heterogeneous catalysts.
First-principles computations were carried out to predict the stability and magnetic and electronic properties of MoS2 nanoribbons with either zigzag- or armchair-terminated edges. Zigzag nanoribbons show the ferromagnetic and metallic behavior, irrespective of the ribbon width and thickness. Armchair nanoribbons are nonmagnetic and semiconducting, and the band gaps converge to a constant value of approximately 0.56 eV as the ribbon width increases. The higher stability of MoS2 nanoribbons, compared with the experimentally available triangular MoS2 nanoclusters, invites the experimental realization of such novel ribbons in true nanoscale.
A selection of recent theoretical and experimental studies on electrolytic hydrogen evolution is presented. It is demonstrated with well-defined model surfaces that this reaction is a very structure-sensitive process. Crystallographic orientation, defect density and surface composition are parameters that determine the local geometric and electronic surface structure, and are thus crucial for the electrocatalytic activity as characterised by the exchange current density. The observed trends can be understood within a recent theory by J. K. Nørskov et al., which is based on density functional calculations and which emphasises the impact of hydrogen chemisorption energies on the reaction rate, that is, on the exchange current density. The particular electrocatalytic activities of ultrathin metal films and of nanostructures are addressed.
Global energy consumption is projected to increase, even in the face of substantial declines in energy intensity, at least 2-fold by midcentury relative to the present because of population and economic growth. This demand could be met, in principle, from fossil energy resources, particularly coal. However, the cumulative nature of CO(2) emissions in the atmosphere demands that holding atmospheric CO(2) levels to even twice their preanthropogenic values by midcentury will require invention, development, and deployment of schemes for carbon-neutral energy production on a scale commensurate with, or larger than, the entire present-day energy supply from all sources combined. Among renewable energy resources, solar energy is by far the largest exploitable resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans in an entire year. In view of the intermittency of insolation, if solar energy is to be a major primary energy source, it must be stored and dispatched on demand to the end user. An especially attractive approach is to store solar-converted energy in the form of chemical bonds, i.e., in a photosynthetic process at a year-round average efficiency significantly higher than current plants or algae, to reduce land-area requirements. Scientific challenges involved with this process include schemes to capture and convert solar energy and then store the energy in the form of chemical bonds, producing oxygen from water and a reduced fuel such as hydrogen, methane, methanol, or other hydrocarbon species.
Activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies
- Li
Molybdenum phosphosulfide: an active, acid-stable, earth-abundant catalyst for the hydrogen evolution reaction
- Kibsgaard